The present invention provides certain improvements in microelectronic device assemblies. The invention has particular utility in connection with configuring circuit boards for use with different microelectronic components or different configurations of microelectronic components
The microelectronic device industry is highly competitive. To maintain a competitive edge, manufacturers must be able to quickly adapt their product lines to advancing technology and changing consumer demands. Many microelectronic products require a number of separate components, one or more of which must be dedicated to a particular product design. If a manufacturer orders an inventory of w microelectronic components dedicated to one particular product, the inventory may have to be discarded or sold well below cost if sales of the product fall short of projected levels.
The memory module industry illustrates the difficulties inherent in, predicting the market and minimizing manufacturing costs. Many computers and other processor-based systems employ either Single In-line Memory Modules (SIMMs) or Dual In-line Memory Modules (DIMMs). SIMMs and DIMMs each generally comprise a circuit board with a plurality of integrated circuit dies mounted thereon. The dies are often interchangeable and can be used on a wide variety of different SIMM or DIMM configurations. The circuit boards, however, are commonly specific to a particular SIMM or DIMM configuration. Manufacturer will order or produce an inventory of circuit boards for a particular SIMM or DIMM configuration. If market demands for that particular configuration fall short of projected demands, the manufacturer will be unable to use the inventory of specialized circuit boards for another memory module product. Oftentimes, if the manufacturer overestimates the demand for a particular memory module configuration, the demand for an alternative configuration will be underestimated. It can sometimes take weeks to redesign and stock an alternative configuration, leading to production delays and backlogs in customer orders.
U.S. Pat. No. 5,377,124 (Mohsen, the teachings of which are incorporated herein by reference) suggests a field programmable printed circuit board which employs a relatively complex, multi-layered circuit board and a specialized integrated circuit die, or xe2x80x9cprogrammable interconnect chip,xe2x80x9d mounted on the circuit board. The programmable interconnect chip includes circuitry which will route connections between the conductive traces provided on the rest of the circuit board. Ostensibly, by replacing one programmable interconnect chip with a different programmable interconnect chip, the circuit board can be adapted for different uses. Unfortunately, designing and producing such specialized integrated circuit dies can be a relatively expensive, time-onsuming process. With some lower profit margin products, e.g., standard memory modules, the cost of such a specialized die may well outweigh the potential cost savings afforded by the adaptability of the basic circuit board.
Manufacturers of memory modules and other microelectronic device assemblies commonly test each module before it is shipped. If one of the integrated circuit dies mounted on the module is defective, the entire module may need to be discarded. In U.S. Pat. No. 5,953,216, the teachings of which are incorporated herein by reference, Farnworth et al. propose an apparatus and method for substituting a replacement device (e.g., a new integrated circuit die) for a defective component (e.g., a defective integrated circuit die). In accordance with this method, the defective component may be isolated by severing electrical connections between the component and the circuit board or the like to which the defective component is mounted. The replacement component may be attached to a replacement site on the circuit board and coupled to a dedicated replacement terminal on the circuit board, e.g., by wirebonding. Farnworth et al. employ a circuit board that includes a replacement site for all of the modules produced, including the majority of the modules that do not include any defective components. Leaving an empty replacement site in defect-free modules may be undesirable in some circumstances.
Embodiments of the invention provide actuatable traces for microelectronic assemblies, selectively configurable circuit boards, processor-based devices employing selectively configurable circuit boards, and methods of selectively configuring a circuit board. An actuatable trace for a microelectronic assembly in one embodiment includes a first conductive length and a second conductive length. A gap is disposed between, and electrically separates, the first and second conductive lengths and has an exposed gap surface. A fusible member is in communication with the gap. The fusible member is spaced from the first and second lengths and is formed of a fusible material which, when melted, will wet the gap surface to electrically connect the first and second conductive lengths across the gap. If so desired, the first conductive length may be formed of a first conductive material and the second conductive length may be formed of a second conductive material, with the fusible material having a melting point below the melting point of the first conductive material and the melting point of the second conductive material.
Another embodiment of the invention provides a selectively configurable circuit board. The circuit board may include a substrate and circuitry carried by the substrate. The substrate may include at least one component site for receiving a microelectronic component. The circuitry may include a plurality of selectively actuatable traces associated with the component site. At least one of the actuatable traces may comprise an actuatable trace in accordance with the previously described embodiment. In one adaptation of such a circuit board, a second one of the actuatable traces can comprise a third conductive length formed of a third conductive material, a fourth conductive length formed of a fourth conductive material, and a gap between the third and fourth conductive lengths. A fused bridge may span the gap to electrically connect the third and fourth conductive lengths. The fused bridge may be formed of a conductive material which is different from, and has a lower melting point than, the third conductive material and the fourth conductive material.
An alternative embodiment of the invention provides a selectively configurable circuit board that includes a substrate having at least one component site adapted to receive a microelectronic component. A plurality of board leads may be adapted to interface the circuit board with an external bus. A plurality of electrical connectors may be arranged adjacent the component site, with the electrical connectors being adapted to be electrically coupled to a contact of a microelectronic component which may be received at the component site. Selectively configurable circuitry may be carried by the substrate and adapted to selectively couple selected ones of the electrical connectors to selected ones of the board leads. The selectively configurable circuitry may comprise at least one trace associated with each of the electrical connectors, with at least one of the traces including a normally open thermally actuatable switch that can be selectively closed to create an electrical connection. The thermally actuatable switch may comprise a gap between two conductive lengths of the conductive trace, an exposed switch surface, and a thermally responsive member that may wet the exposed switch surface when selectively heated above an activation temperature.
A further embodiment of the invention provides a programmable computer that includes a system bus, a processor coupled to the system bus, and a selectively configured circuit board. The circuit board may comprise a substrate having at least one component site and a microelectronic component carried by the substrate at the component site, with the microelectronic component including a plurality of contacts. A plurality of board leads may be coupled to the system bus. A plurality of electrical connectors may be arranged adjacent the component site, with at least some of the electrical connectors being individually coupled to the microelectronic component contacts. A first trace may be carried by the substrate and electrically connect one of the electrical connectors to one of the board leads. The first trace may include a closed switch that comprises a normally open thermally actuatable switch that has been closed to create an electrical connection. A second trace may also be carried by the substrate and coupled to one of the electrical connectors and one of the board leads. The second trace may include an open thermally actuatable switch that can be selectively closed to create an electrical connection.
Still another embodiment of the invention provides a method of manufacturing a microelectronic device assembly including a microelectronic component and a circuit board. Each of a plurality of component contacts of the microelectronic component may be electrically coupled to one of a plurality of board contacts carried by the circuit board. The circuit board may carry a plurality of configurable traces associated with the board contacts and each of the configurable traces may include at least one normally open thermally actuatable switch. A first normally open actuatable switch is identified from the plurality of normally opened thermally actuatable switches. The first switch may be locally heated to selectively close the first switch to define an electrical pathway between at least one of the board contacts and at least one of a plurality of board leads the carried by the circuit board.